Category Science

     It is easier to balance a long pole on the palm than a short stick because of the higher position of the centre of gravity in the former which normally lies near the middle. For balancing a long pole by holding it upright on its end on our palm what we try to do is to keep its centre of gravity right above the base. As long as the centre of gravity remains straight above the base, the stick remains balanced. But being unstable, it tends to fall and the centre of gravity moves away from the vertical. With a long pole we get sufficient time to move our hand to bring its base directly below its centre of gravity thus restoring balance. But with a short stick we hardly get any time to move our palm to restore the balance and the stick falls down.

            We need to wear dark sunglasses in snow-covered areas to prevent damage to our eyes from bright light. Normally our eyebrows cut off the glare from the sky on a bright sunny day. In snow-covered areas, however, the white snow on the ground reflects back most of the sunlight producing a glare of very high intensity. Exposure to such bright light is capable of causing snow-blindness or temporary loss of sight. The use of sunglasses cuts down the glare and helps to prevent damage to our eyes.

A kite flies better without wobbling, spinning or diving if it can keep itself inclined at a specific angle against the blowing wind. This creates a difference in the air-pressure around the kite in such a way that the kite is lifted up. The tail helps a kite in keeping its angle of inclination stable by pulling down its lower tip. Without the tail, wind blowing against the kite and the lift-force generated in turn would send a conventional kite into a tail-spin. Box-kites, however, do not need a tail to stabilize as they do not need to maintain a constant facing angle against the wind to generate the lift. The air swirling through and about a box-kite creates all the pressure differences required to lift up.

            The seconds hand of both quartz and spring watches move in jerks. Only the movement is much more discernible in quartz watches. In spring watches the movement of the seconds hand is guided by the oscillations of the balance-wheel driven by the hair spring. Since the balance wheel oscillates several times a second, the seconds hand in a spring watch appears to move smoothly as the small jerks are almost non-discernible. On the other hand, in quartz watches, the battery powers a stepping motor that moves the second hand in a single step once every second, which can be quite easily made out and the movement appears jerky.

        Another reason for the illusion is the difference in the amount of angular movement each jerk produces in a second hand. In spring watches it is only  whereas in quartz watches it moves by as much as  in a single step.

            Stars are giant glowing balls of fire situated far away from us. Many of them are several times larger than our sun, but being very far away, appear as points of light. Stars themselves don’t twinkle but appear as steady points of light when seen from space where there is no atmosphere. The twinkling of stars as seen from ground is caused by the unsteadiness of the Earth’s atmosphere. When light from an extended source such as the Sun, Moon or the planets pass through the atmosphere, it does not appear to twinkle because the slight changes in apparent brightness in one part is usually compensated by light coming from another part of the celestial object. But when light from a point source like a distant star passes through the atmosphere the fluctuations in the light intensity is not                                                                                       compensated and the star appears to twinkle.